Wet-end molded product

ABSTRACT

An assembly of individual, decoratively embossed fibrous boards having a well-defined, repeating surface pattern, each board of said assembly: 
     (a) being formed by a process comprising the steps of: 
     (i) forming a wet mat of entangled mineral fibers; 
     (ii) pressure molding said fibrous mat while it is still wet to create a decorative textured surface thereon; and 
     (iii) drying said board; and 
     (b) having a higher strength than a board composed of substantially the same amounts of the same ingredients but produced by a dry embossing process.

This is a continuation-in-part of application Ser. No. 754,316, filedJuly 12, 1985, which is a continuation of application Ser. No. 440,042,filed Nov. 8, 1982, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for molding wet-felted fibrousmaterial, and to the molded product produced by this method. Moreparticularly, this invention relates to a method of molding a texturedpattern of high fidelity on a wet-felted, mineral fiber-containing matwhile the mineral fibers are in a wet and highly entangled condition.

2. Description of the Prior Art

The practice of embossing textured patterns and designs on the surfacesof ceiling tiles, ceiling panels and other substrates is widespread andthe art of imparting a decorative appearance to these products isgreatly varied. One basic technique in common usage is to employ anembossing plate or roll which impresses the pattern into the surface ofa dry substrate, thereby often causing the surface to become crushed.Other conventional methods employed, such as cutting, abrading, orrouting out a portion of the surface of the substrate, also involvedeformation of the substrate.

The usual prior art methods of pattern embossing therefore generallyentail the deformation, by pressure or other means, of the substrate. Inthe process, the fibers of the substrate become fragmented. Also, thebinder loses its cohesiveness due to the fragmentation resulting fromthe pressure of the embossing plate or roll. As a result, the substratebecomes weak and vulnerable to humidity and the force of gravity. Thisweakening can cause the substrate to have poor dimensional stability andto sag from the ceiling if it is a ceiling panel or tile.

The current commercial practice in producing textured patterns onmineral board by dry embossing is to emboss a pattern on the dried coreto a depth of about 0.045 inch to 0.065 inch by wetting the dry coresurface with water, and then embossing by means of a hot roll. Due tofracturing of the mineral fibers, a significant loss in core strengthresults. A costly backsizing then is required to restore boardhandleability and high humidity sag properties. However, in the case of"deeply" embossed patterns of 0.100 inch to 0.200 inch, the loss instrength is so large that even backsizing will not help.

Another disadvantage associated with the prior art methods involvingcutting, routing, and abrading is that they produce dust, thus creatinga health and explosion hazard to workers. Complicated and expensive dustcollection systems are required to cope with these hazards.

It would be highly desirable if an improved method of molding a texturedpattern on a substrate could be found which is relatively simple andyields a molded substrate having superior strength and a highly detailedpattern on its surface.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved molded substrate and method, whereby a wet-felted fibrousmaterial containing mineral fibers is subjected to a molding device toyield a molded board having a well-defined pattern.

It is another object of the present invention to provide a molded,mineral fiber containing board which is characterized by excellent boardstrength.

It is still another object of the present invention to prepare a moldedboard product containing mineral fibers by an improved method of moldingwet-felted fibers which minimizes board deformation and avoids to asignificant degree the shearing of fibers and breakage of inter-fiberbonding which occurs during dry molding.

It is a further object of the present invention to provide a new andeconomical method of manufacturing molded, mineral fiber containingboard products, which method is characterized by the ability to quicklychange designs during production and to produce a wide variety ofpattern designs for both commercial and residential applications.

It is a still further object of the present invention to provide anenergy efficient method of manufacturing molded mineral board products,which method is capable of avoiding the costly, energy consuming hotroll embossing involved in dry end embossing.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art when the instant disclosure is readin conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The above objects have been achieved in the molded board product andmethod of the present invention, wherein a wet-felted materialcontaining mineral fibers is molded to yield an embossed board having aparticularly high degree of pattern fidelity. A wet felted matcontaining intermingled mineral fibers is formed by conventional meanson a suitable forming machine, e.g., a Fourdrinier or a cylindermachine. The wet mat which exits from the mat-forming machine isimpressed by a molding roll or other suitable molding means with adecorative textured pattern. Even though the mineral mat containsapproximately 60-70% water by weight, high fidelity patterns areobtained. This is surprising because poor pattern reproduction would beexpected due to the soft and interweaved condition of the wet mat beforemolding.

The molded board of the invention is further characterized by superiorstrength values, which, it is theorized, result from the non-destructiveshaping of the mineral fibers while in the wet, non-rigid state. Thepresent process avoids to a substantial degree the loss in boardstrength associated with the conventional technique of first drying thewet mat before subjecting it to heat and pressure in a subsequentembossing step. The conventional dry embossing process typicallyinvolves the molding of a dried mat (moisture content of less than about5%) by an embossing means, e.g., a molding roll, operating at a pressureof at least about 5-25 pounds per lineal inch, and a temperature of atleast about 500° F. for a brief interval of time, with the applicationof water to the mat prior to molding. Conventional dry embossing isshown in U.S. Pat. No. 4,007,076.

The board of the invention has a significantly higher ultimate strengththan similar boards, i.e. those composed of substantially the sameamounts of the same ingredients, produced by the conventional dryembossing process (defined above). The board made by the wet-end moldingmethod described herein has a transverse strength, as measured by ASTMTest Method C 367, which is at least about 10%, more preferably 40%, andmost preferably 60%, greater than that of a board made by a dryembossing method.

The wet-end method of the invention for producing molded mineralfiberboard typically includes the following steps: forming an aqueoussuspension of the board-forming ingredients; subjecting the aqueoussuspension to a drainage means to form a wet mat; cold pressing the matto further dewater and consolidate it; further pressing the cold pressedwet mat by a patterned roll(s) to produce a molded board; drying themolded board; and fabricating and finishing the board as desired.

DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings in which:

FIG. 1 is a diagrammatic, side elevational view of an apparatus forcarrying out the method of the present invention; and

FIG. 2 is a perspective view of devices for spraying water onto theembossing roll and production line of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The composition to be molded in accordance with the present inventioncontains a mineral fiber component as the essential ingredient thereof.The mineral fiber component includes wool or fibers formed from rock,slag, fused glass, glass mixtures thereof and other heat liquefiable rawmaterials capable of being converted into fibers. The mineral fibersusually have a ratio of length to diameter which is equal to 10 orhigher, with lengths which vary between 0.1 and 100 mm, more typicallybetween 1 and 10 mm, and diameters within the range of 0.1 to 25microns. Mineral fibers having lengths in the range of about 1 to 5 mmhave been found especially useful in the present invention. The moldablecomposition also desirably contains cellulosic fibers and a binder. Thecomposition may comprise about 20% to 85% mineral fibers and about 5% to50%, preferably 15% to 30%, cellulosic fibers, and the binding agent inan amount sufficient to form the embossed board of the invention, as,e.g., about 5 % to 15%.

The cellulosic fibers may be wood fibers, primary or secondary paperfibers, cotton linters or the like. The fiber length will generally beup to about 1/4 inch in length. Highly desirable fibers for use in thepresent invention are newsprint fibers which will generally have alength of from about 1/4 millimeter to about 5 millimeters with anaverage length of about 1 millimeter.

Numerous materials may be used as binding agents in the board-formingcomposition of the invention. Useful binders include starch, chemicallymodified starches, phenol-formaldehyde or other artificial resinbinders, sodium silicate, glue, casein, rubber latex, aqueous rubberdispersions or emulsions, asphalt emulsions, or combinations thereof.

A wide variety of fillers can be employed in the moldable, mineral fibercontaining composition of the invention. The preferred fillers are thosewhich are inorganic. The filler or fillers generally constitute about 5to 70, more preferably about 15 to 50, most preferably about 15 to 40weight percent of the moldable composition. Examples of suitable fillersinclude calcium carbonate, plaster and gypsum, silica, sericite,expanded perlite, natural clay, such as kaolin, bentonite or ball clay,talc, mica and other silicates. Advantageously, the composition containsabout 5% to 50% of expanded perlite particles, which suitably have adensity in the range from about 3.0-8.0, preferably 5.0-8.0, pcf.

The moldable composition additionally may contain other auxiliarysubstances useful in conventional mineral fiberboard-formingcompositions, such as preservatives, wetting agents, defoamers, andflocculents. The amounts of such auxiliary additives can be readilydetermined by those skilled in the art.

A typical formulation for formation of the embossed board of the presentinvention is as follows:

    ______________________________________                                                                          Preferred                                   Ingredient Typical (%) Range (%)  Range (%)                                   ______________________________________                                        Mineral Wool                                                                             49.0        20-85      40-60                                       Clay       11.0        0-20        0-15                                       Perlite    17.0        5-50       15-40                                       Cellulosic Fibers                                                                        15.0        5-50       15-30                                       Starch     8.0         5-15        5-10                                       Flocculent 0.08          0-0.10   --                                          ______________________________________                                    

Referring now to FIG. 1 of the drawings, the mineral fiber containingcomposition of the invention is slurried to a solids content of fromabout 2% to about 6%, and the slurried composition is introduced to headbox 10. The slurry, consisting of about 20% to 90% dry weight offeltable fibers, is subsequently deposited on Fourdrinier wire 11through orifice 12 of head box 10. The first section 13 of theFourdrinier wire permits free drainage of water from the material andfurther drainage is promoted by suction boxes 14 in section 15. As theslurry is brought in contact with the Fourdrinier machine and water ofthe slurry drains therefrom, a wet felted mat of the mineral fibercomposition forms on the machine. The wet laid mat is dewatered by theFourdrinier machine to a solids content of about 15 to 25 weightpercent.

The partially dried material is then prepressed to a thickness of about0.4 to 0.8 inch by a plurality of press rolls 16. It will be appreciatedthat a single set of press rolls could be employed if desired. Afterbeing pressed, the sheet product will generally have from about 50 toabout 75% water. Optimum wet molding results have been achieved when thewet mat moisture before molding is kept below about 69.5%. It is alsopossible to avoid the prepressing operation by molding the wet laid matdirectly after its formation. In another embodiment of the presentinvention, a roll coater 18 may be stationed on the production linebefore the molding device(s) to precoat the wet mat before molding. Thisprecoating may be used to help increase pattern fidelity.

After passing through press rolls 16, the wet mat is then passed viaconveyor rolls 17 to the molding device(s). Various molding means, suchas a patterned plate(s), a molding roll(s), etc., can be utilized toimpress a deep, well-defined, molded pattern into the mat. Roll moldingis found to be a particularly desirable technique because of its speed,economy, and adaptability in permitting pattern changes duringproduction. In practice, the mat is conveyed at a line speed of betweenabout 20 to 50 linear feet per minute between the two rolls 19 and 20.Bottom anvil roll 19 has a fixed axis. Above roll 19 is the molding orembossing roll 20 which has a suitable decorative pattern thereon.Molding roll 20 has its axis vertically movable and control means (notshown) are provided for pressing roll 20 against the moist felted matwhereby the roll's pattern is transferred to the mat. In an alternateembodiment, the top molding roll 20 may be stationary while roll 19moves vertically to adjust the distance between the two rolls. Rolls 19,20 move at a speed that is preferably exactly the same as that at whichthe endless felted mat is being advanced. Molding roll 20 is commonlyunheated, but also can be heated in the range of approximately 100° C.to 400° C. The pressure used in molding roll 20 is typically from about2 to about 50 p.s.i. Pattern detail can be enhanced through increasedroll pressure upon the mineral fiber mat. In a preferred embodiment fora nominal 5/8 in thick product, the wet mat thickness before molding isat least about 0.57 in and a reduction in mat thickness of about 0.04 to0.07 in is effected during the molding operation to ensure good patternreproduction. The method of the invention is capable of yieldingpatterns which are in the range of about 0.025-0.20 in deep.

Molding roll 20 is suitably an iron or steel roll having its outersurface layer provided with the pattern in relief corresponding to theimpression which it is desired to give the wet mat. The patternedsurface layer of roll 20 advantageously comprises any suitable substancewhich, when pressed into the wet mineral fiber-containing mat, resistsany appreciable material pickup and pattern deformation. Both yieldingsurfaces and hard and unyielding surfaces, such as engraved metal, canbe utilized. Preferred cover layers for the molding roll are made of arubber, such as Silastic E RTV rubber available from Dow CorningCorporation, or polyurethane material. Wear of a roll covering made ofpolyurethane or similar material can be minimized by rotating the rollat the speed of the advancing felted mat and exerting only enough rollpressure to produce a good pattern. Manufacture of the patterned coverlayer can be accomplished in a conventional manner, as, e.g., byintroducing the rubber- or urethane-forming ingredients or the like intoa mold and curing the ingredients to form the patterned layer, which isthereafter affixed by conventional means, as, e.g., by a suitableadhesive, such as a rubber contact cement, an epoxy resin adhesive orsimilar resin adhesive, to the molding roll.

As shown in FIG. 2, a suitable device 21 for directing a spray or mistof water 22 onto molding roll 20 is advantageously located above theroll. Water spray pipe 21 can be mounted approximately 18 inches abovemolding roll 20 and operated at about 30 p.s.i. to produce a water spraymist over the molding roll during the molding operation at a rate ofabout 3-4 gal/min. Another spray pipe 21' can be arranged to apply waterto the mat somewhat in advance of molding roll 20. Water application tothe molding roll and/or mat is employed to aid in the clarity and depthof transfer of the molded pattern and to reduce the roughness of themolded surface. The amount of water to be applied can vary over a widerange but generally is from about 30 pounds per thousand board squarefeet to about 80 pounds per thousand board square feet.

After the molding step, the molded product is transferred into dryer 23.At the outlet of the dryer, there is obtained a molded fiberboard havinga moisture content of less than about 0.5%. The dried product can besubjected to any suitable conventional finishing apparatus, depending onthe applications for which it is intended. Such apparatuses include asaw arrangement for cutting the product into smaller panels, applicatorsfor applying coatings to protect and/or decorate the product surface,such as bevel coats, finish spray coats, printing inks, multi-colordecorative coatings, and the like, and further drying equipment.

In accordance with the process of the present invention, the mineralfiber-containing composition is typically formed into a moldedfiberboard of from about 0.4 to 0.8 inch thick, preferably from about0.55 to 0.65 inch thick, and having a density of from about 10 to 25pounds per cubic foot, preferably from about 13 to 18 pounds per cubicfoot.

The present invention provides a novel method to mold deep patterns intomineral lay-in panels using board machine mounted patterned rolls. Boardthickness recovery in the dryer has little effect upon reducing thepattern detail impressed into the wet felted mineral fiber mat by themolding roll(s). The deep impression obtained during the embossment ofthe mat while the mineral fibers are in a wet and highly interlacedcondition is surprisingly maintained in the finished fiberboard eventhough the natural tendency of the indented portions of the fibrousmaterial is to spring back and hence result in shallow, non clear-cutpatterns.

Besides producing a highly decorative, deep textured mineral product,the present process of molding wet felted mineral core helps to reducesignificantly the amount of structural damage caused by dry endfissuring. The method allows for improved final strength of the boardproduced due to actual molding of the fibers to form a pattern shape,thus causing only limited damage to the fibers and to the fiber to fiberbonding. Fissuring and/or embossing of dry, finished core board destroysthis important inter fiber bonding, thereby reducing final boardstrength and resistance to various physical conditions, which may beevidenced, for example, by the sag of panels from a ceiling. The methodof the invention thus yields a molded fiberboard product which ischaracterized by excellent board strength, as evidenced, e.g., in highvalues on breakstrength, good dimensional stability, increased warp andsag resistance, etc. A plurality of the sag-resistant embossed boards ofthe invention will form a highly decorative assembly having awell-defined, repeating surface pattern for use in ceiling structures.

The invention also permits a reduction in the costs of patternproduction, and makes it possible to quickly change pattern designs.This is because the instant molding step can be carried out with the useof an unheated, relatively small diameter roll having a replaceablepatterned covering of rubber, polyurethane or the like. This type ofmolding equipment is much easier and cheaper to replace or modify thanthe heavy, large diameter, engraved metal rolls typically used in dryend embossing. A wide variety of pattern designs, suitable for bothcommercial and residential ceiling products, can be used in forming thedecoratively molded boards of the present invention. Additionally, thepresent method is simple and economical, and is capable of avoiding thehigh energy consumption associated with hot roll embossing.

The process of the invention permits the manufacture of products withembossed surfaces having highly decorative three dimensional patterns.These surface patterns have the variety, definition, accuracy andfidelity only previously attained by the process of hot embossing withsteam or moisture on a cured and dry substrate. The inventive processmakes possible a pattern selection from finite continuous-depressedlinear and geometrical elements to broad surfaced sharply definedcharacters.

All other known products whose surface pattern or decoration is appliedin the wet or uncured state lack the combination of important surfacecharacteristics of the inventive boards, which include good definition,pattern repeatability, and top surface smoothness. The combination ofsuch properties is unattainable by those processes producing simulatedfissured and crater-like surfaces or other discontinuous textures, suchas the process of U.S. Pat. No. 4,263,093. The board produced accordingto this patent cannot have an accurately defined repeating pattern asthe pattern is applied by a needle roll and not a continuous embossingmeans such as is employed in the present invention. Also, the additionof a perlite covering layer and further processing will inherently alterthe surface pattern in a random and uncontrollable manner. The patternsachieved by this method can only be random, rough textured, andfissured/crater-like surfaces.

The present invention is further illustrated by the following example inwhich all percentages are by weight.

EXAMPLE

This example illustrates with reference to FIGS. 1 and 2 of the drawingsthe production in accordance with the present invention of wet-moldedfiberboard containing mineral fiber.

The formulation utilized in manufacturing the product of this inventionconsisted of the following ingredients in the listed percentages byweight:

    ______________________________________                                               Ingredient                                                                              %                                                            ______________________________________                                               Mineral Wool                                                                            50.4                                                                Clay      6.4                                                                 Perlite   19.7                                                                Newsprint 14.9                                                                Starch    8.6                                                          ______________________________________                                    

The ingredients were diluted with water to form a slurry, and the slurrywas deposited on Fourdrinier wire 11. The slurry was dewatered in aconventional manner on the Fourdrinier machine to form a wet felt or matof interlocked fibers. The partially dewatered fibrous mat was nextpassed through a press section comprising pressing rolls 16, whichdensified the mat and provided a wet mat of uniform thickness (about0.57 inch) with a moisture content of about 69.5%.

After leaving the press section, the wet mat was passed on rollerconveyors 17 between molding roll 20 and anvil roll 19. Molding roll 20was a 15 inch diameter steel roll and its roll surface consisted of apatterned 70 durometer polyurethane cover having a thickness of about0.38 in. Enough downward roll pressure was applied to the mat to obtainthe desired pattern fidelity, but not so much as to cause mat distortionor cracking. A highly decorative, 0.125 in deep pattern was impressedinto the board by molding roll 20. During the run, compressed air atrelatively low pressure was occasionally directed at the molding roll tokeep it clean and sharp. Rolls 19, 20 were rotated in the board-formingdirection (in the direction of the arrows shown in FIG. 1), and at thesame speed as the forming line. The wet board thickness after impressionby molding roll 20 was about 0.53 inch.

The molded board was conveyed from molding roll 20 to dryer 23. Afterbeing dried, the board product was subjected to various conventionalfinishing steps, including cutting into appropriate sizes, cleaning,base coating by a Steinemann coater, and further drying and cleaning. Anafterspray coating was next laid down on the board and this coating wasdried. Finally, the cooled board was cut into panels and packaged forthe marketplace.

Wet molded lay-in panels made in accordance with the foregoing procedurehad the following physical properties:

    ______________________________________                                        Thickness, in          0.57                                                   Density, lb/cu ft      16.0-18.0                                              Transverse Strength, lb                                                                              42                                                     ______________________________________                                    

Whereas the present invention has been described with respect tospecific embodiments thereof, it should be understood that the inventionis not limited thereto as many modifications thereof may be made. It is,therefore, contemplated to cover by the present application any and allsuch modifications as fall within the true spirit and scope of theappended claims.

I claim:
 1. An assembly of individual, decoratively embossed fibrousboards having a well-defined, repeating surface pattern, each board ofsaid assembly:(a) being formed by a process comprising the steps of:(i)forming an aqueous slurry of entangled mineral fibers; (ii) dewateringsaid slurry to form a wet mat; (iii) pressing said wet mat toconsolidate said mat, said consolidated wet mat having from about 50 to75% water; (iv) pressure molding said consolidated wet mat at a pressureof about 2 to 50 psi while it is still wet by a molding means providedwith a patterned surface layer to create a decorative textured surfaceon said consolidated wet mat; and (v) drying said board; and (b) havinga higher strength than a board composed of substantially the sameamounts of the same ingredients but produced by a dry embossing process.2. The assembly of claim 1 wherein said wet mat comprises, on awater-free basis, about 20 to 85 weight percent of mineral fibers, 5 to50 weight percent of cellulosic fibers, and 5 to 15 weight percent ofbinder.
 3. The assembly of claim 1 wherein said wet mat, on a water-freebasis, comprises:(a) about 20 to 85 weight percent of mineral wool, (a)about 0 to 20 weight percent of clay, (c) about 5 to 50 weight percentof perlite, (d) about 5 to 50 weight percent of cellulosic fiber, (e)about 5 to 15 weight percent of starch, and (f) about 0 to 0.1 weightpercent of flocculent.
 4. The assembly of claim 1 wherein said step (ii)is accomplished by continuously dewatering said aqueous slurry of saidstep (i) on a moving porous carrier capable of passing drainable watertherethrough and retaining solids thereon.
 5. The assembly of claim 4wherein said pressure molding step (iv) is accomplished by rollingpressure of a molding roll.
 6. The assembly of claim 5 wherein, beforesaid pressure molding step (iv), a paint coating is applied to the faceof said consolidated wet mat.
 7. The assembly of claim 5 wherein wateris applied to the surface of said molding roll during said pressuremolding step (iv).
 8. The assembly of claim 5 wherein, before saidpressure molding step (iv), water is applied to the face of saidconsolidated wet mat.
 9. The assembly of claim 5 wherein said moldingroll has a patterned surface layer composed of a material selected fromthe group consisting of rubber, polyurethane and metal.
 10. The assemblyof claim 5 wherein said molding roll is heated in the range of about100° to 400° C.
 11. The assembly of claim 1 wherein said wet matcomprises, on a water-free basis, about 20 to 85 weight percent ofmineral fibers, 5 to 50 weight percent of cellulosic fibers, 5 to 70weight percent of fillers, and 5 to 15 weight percent of binder.
 12. Theassembly of claim 11 wherein said step (ii) is accomplished bycontinuously dewatering said aqueous slurry of said step (i) on a movingporous carrier capable of passing drainable water therethrough andretaining solids thereon.
 13. The assembly of claim 12 wherein saidpressure molding step (iv) is accomplished by rolling pressure of amolding roll.
 14. The assembly of claim 13 wherein water is applied tothe surface of said molding roll during said pressure molding step (iv).15. The assembly of claim 13 wherein, before said pressure molding step(iv), water is applied to the face of said consolidated wet mat.
 16. Theassembly of claim 13 wherein said molding roll has a patterned surfacelayer composed of a material selected from the group consisting ofrubber, polyurethane and metal.
 17. An assembly of individual,decoratively embossed fibrous boards having a well-defined, repeatingsurface pattern, each board of said assembly:(a) being formed by aprocess comprising the steps of:(i) forming an aqueous slurry of solidsand water; (ii) dewatering said slurry to form a wet mat; (iii) rollpressing said wet mat to consolidate said mat; (iv) subjecting saidconsolidated wet mat to rolling pressure of a molding roll to create adecorative textured surface thereon; and (v) drying said board; and (b)having a higher strength than a board composed of substantially the sameamounts of the same ingredients but produced by a dry embossing process.18. The assembly of claim 17 wherein said wet mat comprises, on awater-free basis, about 20 to 85 weight percent of mineral fibers, 5 to50 weight percent of cellulosic fibers, 5 to 70 weight percent offillers, and 5 to 15 weight percent of binder.
 19. The assembly of claim17 wherein said wet mat, on a water-free basis, comprises:(a) about 20to 85 weight percent of mineral wool, (b) about 0 to 20 weight percentof clay, (c) about 5 to 50 weight percent of perlite, (d) about 5 to 50weight percent of cellulosic fiber, (e) about 5 to 15 weight percent ofstarch, and (f) about 0 to 0.1 weight percent of flocculent.
 20. Theassembly of claim 19 wherein said solids of said slurry comprise:(a)about 40 to 60 weight percent of mineral wool, (b) about 0 to 15 weightpercent of clay, (c) about 15 to 40 weight percent of perlite, (d) about15 to 30 weight percent of newsprint fibers, (e) about 5 to 10 weightpercent of starch, and (f) about 0 to 0.10 weight percent of flocculent.